on a very small (or large) version, do not index

[rjbs]

Really, this should become a useful user message, but it's painfully difficult to get that error up through the call stack. This code needs (in my opinion) to be rearchitected to make this sort of thing simple.

In the meantime, the code now detects this case specifically, so we can do something about it later.

Meant to help with #192, but won't help enough until we can get the message passed upward.

[andk]

@rjbs, could you please review and fix the conflicts?